Method of refining crude olefinic nitriles



july 16, 1946.

Filed oci. 31; 1959 WAH? -L man? E. L. CARPENTER ETAL METHOD OF REFINING CRUDE OLEFINIC NITRILES FIG. l.

3 Sheets-Sheet 1 I SFPA P4 To@ JA'PAIPATO? f 'crap/ mf l 1NVENTOR5 ATTORNEY.

July 16, 1946.

E. L. CARPENTER ET Al. 2,404,163

METHOD OF REFINNG CRUDE OLEFINIC NITRILES Filed Oct. 3l, 1939 3 Sheets-Sheet 2 LD/JCHR.

July 16, 1946. E. L. CARPENTER E1A L 2,404,163

METHOD 0F RE'FINING CRUDE OLEFINIC NITRILES Filed ou. s1, 193s s sheets-sheet s ATTORNEY.

i tem. A

. As shown in Fig. l, afquantity of 'a crude oleflnic nitrile. such as, for example, a crude product of acrylonitrile and water produced, for instance,

Patented `16 1946 UNITED s'rA'rss PATENT: ori-*ics o :iWE'IHOD.0F REm'lNBEgRUDE-OLEFINIC o of Maine Application October 31, 1939, Serial' No. 302,072

The present invention relates to the refining of crude oletlnic nitriles, that is, those nitriles which may be hydrolyzed to olenlc acids.

'I'he dehydration of an alkylene cyanohydrin yields equi-molecular proportions of the corresponding olefinic nitrile and water, which may be collected as two partially miscible layers. Upon separation, the upper layer is `found to be predominantly nitrile containing some Water, while the lower is predominantly water containing some nitrile.

For instance, in the production of acrylonitrile from the dehydration of ethylene cyanohydrin, the upper nitrile layer of the product is found to contain from4 to 5% of water whereas the lower or water layer may contain from 5-8% of nitrile.

Therefore, in the manufacture of the olefinic 'nitriles, it is highly essential to have at hand a resides in a method of refining a crude olefinicv 13 Claims. (Cl. 20E-42) nitrile wherein the product may -be readily ob'- l tained free fromwater. Another important object is to provide an oleflnic nitrile in a pure state by a method requiring only simple apparatuswith high eillciencies. l

The applicants have discovered that olefinicnitriles saturated with water, distill azeotropically in such proportions that the .percentage by weight of water in the distillate exceeds .the solubility of water in the nitrile. and consequently the distillate separates into two layers. Hencea largel proportion ofjthe water may be removed from the saturated solution by' placing a water separator in the head of a reflux column and continuously reuxlng the solution. As the water is removed from the solution, the percentage of of water remaining in the nitrile removed by distillation. This procedure has the advantage of reducing the volume of the fore-runnings toa very considerable extent.

f Referring to the accompanying drawings,

Fig. 1 .is a diagrammatic ilow sheetvof a preferred method of carrying out theinvention;

ll'lg. 2 shows a modied method, and

Fig. 3 illustrates still another alternative sysby the dehydration of ethylene cyanohydrin, is permitted to separate into two layers. The lower layer of water containingfrom 5 'to 8% of acrylonitrile is withdrawn and shaken with about twice its volume of xylene. The mixture separates into two layers upon standing. The lower layer, being principally water, isj withdrawn and discarded. The upper xylene layer containing the acrylonitrile is united with the initial acrylonitrile layer containing from 4 to 5% water. The xylene displaces a small amount of water from the mixture. This water layer is withdrawn and returned to an initial water layer containing some acrylonitrile.- The remaining layer of acrylonitrile, xylene and dissolved water is fractionated in a fractionating still operating with substantially total reflux of the nitrile. 'I'he Water and nitrile form an azeotropic mixture in the reflux column.

.Over a temperatureY range of from 70 to.75 C.`

this reux mixture is condensed at the retlux head and allowed to' stratify into two layers. The upper nitrile layer flows -back into the still while the lowerfwater layer is-Withdrawn and returned to an initial water layer containing some acrylonitrile. A small amount of nitrilepolymer forms As illustrated by the flow sheet of Fig.2, a nuan-v tity of a crude olefinic nitrile such as. for examv ple, a crude product of acrylonitrile and water, f producedasv above, is permitted to separate into vtwo layers. The lower layer of` waterfcontaining lfrom 5 to 8% of acrylonitrile is withdrawnzand ol vThe mixture upon standing separates into two layers. The lower layer being principally water shaken with .about twice its volume of xylene.

'l is withdrawnv and discarded. The acrylonitrile is removed from the upper xylene layer bydistillation. .The still residue of polymer and xylene is illtered and the-'latterreturned to the cycle. f Thelnitial acrylonitrile layer containing from aA temperature range of from ,70 to 75 C. thisk the lower water layer is withdrawn and returned to an initial'water layer containing some acrylonitrile. A small amount of nitrile polymer forms during the fractionation. The acrylonitrile from the xylene extraction of the initial water layer is added to the still content. A fraction of wet acrylonitrile is then removed at a temperature of from 75 to 77 C. and returned to an initial acrylonitrile layerl containing water. The dry acrylonitrile is distilled from the polymer residue at a temperature of from 77 to 78 C.

- In reiining a crude olenic nitrile such as, for example, crude acrylonitrile, as illustrated by the ilow sheet of Fig. 3, the .crude product is allowed to separate into two layers. The lower layer of 'water containing some nitrile is withdrawn and discarded. The upper acrylonitrile layer containing some ,water is fractionated in a fractionating still operating with substantiallyy total reux of the nitrile. The water and acrylonitrile form an azeotropic mixture in the reflux column. Over a temperature range of from 70 to'75 C. this mixture is condensed at the reflux head and allowed to stratify into two layers. The upper nitrile layer flows back into the still while the lower water layer is withdrawn and discarded. A fraction of wet acrylonitrile is then removed at a temperature of from 75 to 77C. and returned to an initial acrylonitrile layer containing water.

" The dry acrylonitrile is distilled from the polymer residue at a temperaturev of from '77 to 78 C.

In employing theprocedure outlined by the flow sheet of Fig. 3, a crude crotonic nitrile-water mixture, produced for instance by the dehydration of propylene cyanohydrin, is` permitted to separate into two layers. The lower layer of water containing some crotonic nitrile is withdrawn and discarded. The upper layer which is predominantly crotonic nitrile containing some water is dried by azeotropic distillation from a fractionating still. The water and crotonic nitrile form an azeotropic mixture boiling ata temperature yof about 85 C. which is condensed at the reflux head of the still and permitted'to stratify into two layers. \The upper crotonic nitrile layer is returned to the still while the lower water layer is removed and discarded. The cisand trans-crotonic nitrile isomers are thereafter fractionally distilled from the stillcontent at the temperatures of 107.5-108.5 C. and 119.0120.5 C. respectively.

Olenic nitrile solventswhich'are immiscible with water, such as benzene, toluene, xylene and the like are suitable for the extraction of the oleiinic nitrile from the water layer.

Other members of the oleiinic nitrile series in similar crude form maybe refined according `to the method herein described, using appropriate temperatures dependent upon the nitrile chosen.

While the invention has been described with particular reference to specific embodiments, it is to be understood that it is not to be limited thereto but is to be construed broadly and restricted solely by the scope of the appended claims. 1

We claim:

yl. 'Avmethod of refining a crude olenic nitrile containing' water which comprises separating the product into two layers, the upper of which is predominantly nitrile containing some water while the lower layer is predominantly water containing some nitrile, extracting the nitrile from said lower layer by means of a hydrocarbon solvent, combining the solvent extract and upper nitrile layer, permitting the mix to stratify, re-

produced initial water layer containing nitrile,

subsequently fractionally distilling a. wet nitrile fraction from the hydrocarbon solvent-nitrile mixture and returning said nitrile fraction to a subsequently produced initial nitrile layer containing water, thereafter fractionally distilling the dry oleiinic nitrileffrom the hydrocarbon solvent-polymer residue, -separating the polymer and hydrocarbon solvent, and returning the latter to the .cycle for extraction of nitrile from a subsequently produced and initial lower layer predominantly water but containing some nitrile.

2. A method of refining crude acrylonitrile containing water which comprises separating the product into two layers, the upper of which is prei dominantly acrylonitrile containing some water while the lower layer is predominantly water containing same acrylonitrile, extracting the acrylonitrile from the said lower layer by means of xylene, combining the xylene extract and upper acrylonitrile layer, permitting the mix to stratify. removing the lower water layer displaced by the xylene and returning the same to a subsequently produced initial water layer containing acrylonitrile, distilling the major portion ofthe remaining water from Vthe xylene-acrylonitrile mixture at a temperature of from 70 to 75 C., and returning the said water distillate to the above andy subsequently produced initial water layerl containing acrylonitrile, subsequently fractionally distilling awet acrylonitrilel fractionv from the xylene-acrylonitrile mixture at a temperature of from 75 to '77? C., and returning said acrylonitrile fraction to a subsequently produced initial acrylonitrile layer containing water, thereafter fractionally distilling the dry acrylonitrile from the xylene-polymer residue at a temperature of from 77 to 78 C., separating the polymer and'xylene and returning the latter to the cycle for extraction of acrylonitrile from a subsequently Iproduced and initial ylower layer predominantly water but containing some acrylonitrile.

3. A method `of reilning a crude oleflnic nitrile containing water which comprises separating the product into two layers, the upper of which is predominantly nitrile containing some water while the lower la'yer is predominantly water containing some nitrile, extracting the nitrile from said lower layer by means of a hydrocarbon solvent, distilling the nitrile from the hydrocarbon solvent, separating the still residuev of polymer and hydrocarbon solvent and returning the latter to the cycle, distilling the major portion of "the water from tlieinitially produced upper nitrile layer and returning said` water distillate to a subsequently produced initial water layer containing nitrile, adding to the nitrile layer remaining from the major water removal step, the nitrile from the hydrocarbon solvent extract to form a-nitrile mixture, subsequently fractionally distilling a wet nitrile fraction from the said nitrile mixture and returningsaid nitrile fraction to an initial nitrile layer containing water, thereafter fractionally distilling the dry oleiinic nitrile from the polymer residue.

4. A method of refining crude acrylonitrile containing water which comprises separating the` product into two layers, the upper of which is predominantly acrylonitrile containing some water while the lower layer is predominantly water containing some acrylonitrile, extracting the acrylonitrile from the said lower layer by means of xylene, distilling the acrylonitrile from the xylene, separating the still residue of polymer and xylene and returning the latter to the cycle, distilling the major portion of the water from the upper acrylonitrile layer at a temperature of from 'I0 to 75 C. and returning said water distillate to a subsequently produced initial water layer containing acrylonitrile, adding to the remaining acrylonitrile layer the acrylonitrile from the xylene extract to form an acrylonitrile mixture, subsequently fractionally distilling a. wet acrylonitrile fraction from the acrylonitrile mixture at a temperature of from 75 to 77 C. and returning said acrylonitrile fraction to an initial acrylonitrile layer containing water, thereafter fractionally distilling the dry acrylonitrile from the polymer residue at a temperature of from 77 to '78 C.

5. A method of refining a crude olenic nitrile containing water which comprises separating the product into two layers, the upper of which is predominantly nitrile containing some water while the lower layer is predominantly water containing some nitrile, distilling from the upper nitrile layer an azeotropic mixture of nitrile and water, subsequently fractionally distilling a wet nitrile fraction therefrom and returning the same to a subsequently produced initial nitrile layer containing water, thereafter 4distilling the dry olenic nitrile from the polymer residue.

6. A method of refining crude acrylonitrile containing water which comprises separating the product into two layers, the upper of which is predominantly acrylonitrile containing some water while the lower layer is predominantly water containing some acrylonitrile, distilling from the upper acrylonitrile layer an azeotropic mixture of acrylonitrile and water until the distillate temperature has risen from 70 C. to '75 C., subsequently fractionally distilling a wet acrylonitrile fraction therefrom at a temperature of from 'l5-77 C. and returning the same to a subsequently produced initial acrylonitrile layer containing water, thereafter distilling the dry acrylonitrile from the polymer residue at a temperature of from 77 to '78 C.

'1. A method of refining crude crotonic nitrile containing water which comprises separating the product into two layers, the upper of which is predominantly crotonic nitrile containing some water while the lower layer is predominantly water containing some crotonic nitrile, distilling from the upper crotonic nitrile layer an azeotropic mixture of crotonic nitrile and Water until the crude crotonic nitrile is substantially dehydrated, subsequently distilling a wet crotonic nitrile fraction therefrom to remov.. the remaining Water and returning this fraction to a subsequently produced initial crotonic nitrile layer containing water, and thereafter fractionally distilling the cisand trans-crotonic nitrile isomers at the temperatures of 107.5108.5 C. and 119.0-120.5 C. respectively.

8. A method of refining a crude olenic nitrile containing water to remove water therefrom which comprises distilling therefrom an azeotropic mixture of the nitrile and water, condensing the distillate, permitting the condensed distillate to stratify into an upper wet nitrile layer and a lower water layer. separating et! the water layer, returning the wet nitrile layer to the distilland for recycling and finally collecting the substantially dehydrated nitrile.

9. A method of refining a crude acrylonitrile containing water to remove water therefrom which comprises distilling therefrom an azeotropic mixture of the acrylonitrile and water, condensing the distillate, permitting the condensed distillate to stratify into an upper wet acrylonitrile layer and a lower water layer, separating off the water layer, returning the wet acrylonitrile layer to the distillandv for recycling and nally collecting the substantially dehydrated acrylonitrile.

10. A method of refining a crude crotonic nitrile containing water to substantially dehydrate the same which comprises distilling therefrom an azeotropic mixture of the crotonic nitrile and water, condensing the distillate, permitting the condensed distillate to stratify into an upper wet crotonic nitrile layer and a lower water layer, separating olf the waterlayer, returning the wet crotonic nitrile layer to the distilland for recycling and finally collecting the substantially dehydrated crotonic nitrile.

11. In the method of refining a crude oleiinic nitrile vcontaining water to substantially dehydrate the mixture, the process which comprises placing the crude nitrile in a still provided with a fractionating column and a condenser, distilling an azeotropic mixture of nitrile and water from the crude nitrile, passing the vapor distillate through the fractionating column and into the condenser, condensing the distillate,' allowing the distillate t0 stratify into an upper nitrile layer substantially saturated with water,A and a lower water layer, drawing oif the water layer, and returning the wet nitrile to the fractionating column, and finally collecting the substantially dehydrated nitrile.

12. In the method of refining a crude acryloriitrile containing water to substantially dehydrate the mixture, the process which comprises placing the crude acrylonitrile in a still provided with a fractionating column and a. condenser, distilling an azeotropic mixture of acrylonitrile and water from the crude acrylonitrile, passing the vapor distillate through the fractionating column and into the condenser, condensing the distillate, allowing the distillate to stratify into an upper acrylonitrile layer substantially saturated with water, and a lower water layer, drawing ofi` the water layer, and returning the wet acrylonitrile to the fractionating column, and finally collecting the substantially dehydrated acrylonitrile.

13. In the method of refining a crude crotonic nitrile 4containing water to substantially dehydrate the mixture, the yprocess which comprises placing the crude crotonic nitrile in a still provided with a fractionating column and a condenser, distillng an azeotropic mixture of crotonic nitrile and water from the crude crotonic nitrile, passing the vapor distillate through the fractionating column and into the condenser, condensing the distillate, allowing the distillate to stratify into an upper crotonic nitrile layer substantially saturated with water, and a lower water layer, drawing olf the water layer, and returning the wet crotonic nitrile to the fractionating column, and iinally collecting the substantially dehydrated crotonic nitrile.

ERWIN L. CARPENTER. HAaoLD s. DAVIS. oscm F. Winsum/IAN. 

